Self-contained device for controlling limit temperature during the transport of perishable foodstuffs

Abstract

Self-contained device and method for determining the variations in temperature regulated temperature enclosures. The device consists of a container comprising a tank connected to a receptacle, the inner spaces of which communicate with one another through one or two ducts of reduced or constricted cross sections. Said container is formed at least partially, of a material allowing heat transfer with the exterior and contains an intially solidified material, the melting temperature thereof being constant and the total volume being less than or equal to the overall volume of the tank and duct element.

I claim: 
     
       1. An autonomous device which checks for temperature deviations in a controlled-temperature enclosure, comprising a container comprising a reservoir connected to a receptacle whose internal spaces communicate with one another via two conduits having a smaller cross section, said container being at least partly formed by a material allowing heat exchange with the outside;   at least one filling means for filling the container; and   a content consisting of a solidified substance whose melting temperature is constant and whose total volume is less than the overall volume of the reservoir, wherein the reservoir is provided with a retaining means to maintain the substance in the solid state, the retaining means consisting of a plate provided with perforations or asperities, and of a surface approximately perpendicular to the direction of gravity and whose perimeter is such that the melted substance can flow into the receptacle along the wall of a the reservoir without the risk of directly blocking the two conduits.     
     
     
       2. The device according to claim 1, wherein one of the conduits enables the substance to flow from the reservoir into the receptacle and the other conduit enables the air in the receptacle to flow into the reservoir. 
     
     
       3. The device of claim 1 wherein said device is employed such that the reservoir is approximately plumb with the receptacle, it being possible for the receptacle in turn to become the reservoir, and vice versa, by turning the device upside down or pivoting the device through 180°. 
     
     
       4. The device according claim 1, wherein the means for filling the container is either an orifice capable of being plugged or a leaktight system for fixing the receptacle to the reservoir. 
     
     
       5. The device according to claim 1, wherein the substance is a eutectic and has a melting temperature which lies between -30° and +20° C. 
     
     
       6. The device according to claim 1, wherein the reservoir and the receptacle are made of a transparent or translucent material of a plastic or composite type. 
     
     
       7. The device according to claim 1, wherein, the connecting conduit is made of a material having a high thermal conductivity, said material being selected from the group consisting of a metal, a metal alloy, a plastic or a combination of thereof. 
     
     
       8. The device according to claim 1, wherein the conduit is completely filled with said substance. 
     
     
       9. The device accordingly to claim 1, wherein the receptacle includes graduations enabling the volume of substance which has flowed from the reservoir into the receptacle to be measured, said volume being a direct function of the product Δt to Δθ, Δθ representing the temperature difference between the ambient temperature and the mailing temperature of the substance, Δt representing the time during which Δθ is positive. 
     
     
       10. A method of checking that the temperature in a controlled-temperature enclosure has been maintained between times t 0  and t 1 , said method comprising the steps of: a) putting into said enclosure an autonomous device according to claim 1 wherein the material has a melting temperature chosen depending on the controlled temperature required, said substance being initially, at time t 0 , in the entirely solid state in the reservoir and in the conduit;   b) observing, at time t 1 , the presence or absence of said substance in the receptacle; and   c) measuring the quantity of said substance in the receptacle, wherein said measurement is correlated with temperature excursions in the enclosure at at least certain moments between times t 0  and t 2 .   
     
     
       11. The method according to claim 10, wherein the melting temperature of the substance is greater than or equal to the maximum temperature allowed for preservation of said perishable goods. 
     
     
       12. The method according to claim 10, wherein the reservoir and the receptacle are made of a transparent to translucent material of a plastic or composite type. 
     
     
       13. The method according to claim 10, wherein at time t 0  the conduit is filled with the substance. 
     
     
       14. The method according to claim 10, wherein the difference in pressure between the receptacle and the reservoir is zero, the flow of the substance from the reservoir into the receptacle being compensated for by air in the receptacle escaping into the reservoir. 
     
     
       15. The method according to claim 10, wherein the device has a geometry characterized by a ratio between a surface for heat exchange with the controlled temperature enclosure and a volume of substance determined as a function of the product (Δt×Δθ) at which it is desired to detect, Δθ, being the temperature excursion between the maximum temperature allowed in the enclosure and the melting temperature of the material, Δt being the duration of the temperature excursion Δθ. 
     
     
       16. The method according to claim 10, wherein the volume of material collected in the receptacle is a function of the product (Δt×Δθ); Δθ representing the temperature difference between the ambient temperature and the melting temperature of the substance; and Δt representing the time during which Δθ is positive. 
     
     
       17. The method according to claim 10 wherein the longer the Δt values it is desired to detect, the greater are the reservoir and receptacle volumes chosen. 
     
     
       18. The method according to claim 10, wherein, in the case of an observed transfer of substance from the reservoir into the receptacle during an operation to monitor compliance with the temperature standards, said device, after complete liquefaction of the still solid substance contained in the reservoir and then solidification, is used for another monitoring operation, as long as the receptacle, then filled with solid substance, is used as the reservoir and the old receptacle, then empty, as the reservoir. 
     
     
       19. The method according to claim 10, wherein one or more devices are used in a given controlled-temperature enclosure, each device itself being characterized by a defined melting temperature of the substance. 
     
     
       20. The method according to claim 10 wherein said one or more devices may furthermore be combined with another system of checking the temperature. 
     
     
       21. The method according to claim 10, wherein a device according to claim 1 is used with a telltale device consisting of a reservoir made of a material allowing heat exchange with the outside and of a content made of a solidified material which has a constant melting temperature and is held in place in the upper part of the reservoir. 
     
     
       22. The method of claim 20, wherein said another system of checking the temperature is a recording thermometer, a self-adhesive indicator, or a heat-sensitive ink.